Radiating system



Nov. 26, 1946. w. P. MASON RADIATING SYSTEM Filed Aug. 19, 1941 FIG. 24

FIG/ 4 FIGS FIGS

FIG 6' w alpwy aasmwaenwwx q/ q/alq INVENTOR W P MASON %1 ATTORNEY Paienieol- Nov. 2d. lddd I 2,411,551 Rapm'rmo SYSTEM Warren P. Mason, West Orange, l l. .L, assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 19, 1941, Serial No. 407,457

.4 Claims. i

This invention relates to improved directional compressional wave radiating systems of the multielement type. More particularly it relates to radiating systems in which the energy is dis-: tributed non unlformly over the elements of the radiating system to reduce the relative strength of secondary radiation lobes with respect to the main radiation lobe.

A-principal object of the invention is therefore to produce directional radiating systems having relativelysrnall secondary radiation lobes.

Another object of the invention is to reduce secondary lobe radiation from multicrystal radiating systems. I

A furtherobject is to reduce secondary lobe radiation from multiunit magnetostrictive radiating systems.

Other and further objects will become apparent during the course of the following description and in the appended claims.

lhe systems of the invention will be more readily understood from the following description of illustrative embodiments taken in conjunction with the accompanying drawing in which:

Fig. 1 illustrates a radiating element of sub-v stantial surface area uniformly driven;

Fig. 1a indicates the directive radiating pattern of the surface of Fig. 1;

Fig. 2 illustrates a radiating element of substantial surface area driven with straight line variation of intensity from zero intensity at the ends to maximum intensity at the center;

Fig. 2a indicates the directive radiating pattern of the surface or Fig. 2;

Fig. 3 illustrates a radiating element of sub- 2- stantial surface area driven with sinusoidal variation of intensity from zero intensity at the ends to maximum intensity at the center;

Fig. 4 shows a radiating system comprising a plurality of piezoelectric crystals aligned to form a multielement radiating surface, the driving electrode areas of said crystals varying from very narrow areas for the outermost crystals to substantially complete coverage of the central crystal; Fig. 5 shows a radiating diaphragm of substan tial surface area driven by a plurality of magnetostrictive vibrators, the driving intensity varying from small intensity at the outermost vibrators to maximum intensity at the center vibrator; and

Fig. 6 shows a sound radiator of the multisection wave filter type with energy radiation provided from each section of the structure.

In more detail in Fig. 1 a member or diaphragm I0 is assumed to be driven from position a to position b with uniform amplitude at all points thereof. This may be accomplished, for example, by the well known electromagnetic type of driving mechanism employed in the so-called dynamic type ofloudspeaker such as, f1

disclosed in United States Pat sued May 7, 1929, to A. I. Abral driving mechanism is not show it would unnecessarily compli Such mechanisms are well knov are not involved in systems of will become apparent presently. For radiating surfaces of the by member ill of Fig. 1, characte where his the length or width is 21r times the frequency, v i propagation in the medium, 0 i: ured between the direction of t length of the radiator as show the pressure at the angle a, an sure normal to the radiator. Tl. that if most of the radiation within i1 from the normal, ti be about 5'7 wave-lengths across plications would be inconvenie1 Also, secondary lobes will exi wL cos 0) 2 etc, whose values compared to 2 1 .3 2 13.5 db., 17.9 (11).,

The first lobe is only 13.5 dei pared to the main one and ma tioned, introduce some difiicu readings.

A method for reducing secc respect to the main one is discu 2,225,312, issued December 17, thereof, column 1, line to r lines a and b indicating the mode of vibration of diaphragm For this distribution the radia tion patter-n illustrated by curve 22 of Fig. 2a and is given by the equation Fer this distribution the first minimum comes at twice the angle as for the uniform distribution of Fig. 1, but the secondary lobes are down compared to the fundamental by the values 2 h (r) =41.c db., etc. 4 Hr To get the same sharpness requires a radiator with twice the length, but all the radiation maxima are down as far in decibels as for the uniform radiator.

A radiator in which the secondary maxima are not down quite as far, but which requires only a 50 per cent larger radiator to get the some sharpness is shown in Fig. 3. For this radiator the particle velocity of diaphragm it is substantiallyzero on the two ends and has a sine wave distribution of particle velocity between dotted lines a and 1; indicating the mode of vibration of diaphragm- 36. A sine wave distribution of energy as applied to a multitube directive acoustic receiver isdiscussed and analyzed in my abovementioned Patent 2,225,312 on pages 2 and 3 thereof; page 2, column 2, line 48 to page 3, column 1, line iii. In the device of the patent the areas of the respective tubes, or their orifices, are varied substantially in accordance with a sinusoidal lawof variation. In this particular instance the row of tubes is wound about itself to form a compact assembly so that the tubes may be more readily associated with a. conventional type of receivcr niicrophone and to facilitate the pointing of the'ossembly. For the type of radiator illustrated by Fig. 3 and the arrangement of my patent just mentioned the distribution pattern is given by the equation a PM) l- (:5 cos 0) The first minimum comes when cos 9 (6) which is 50 per cent larger than that of Fig. 1, but the secondary lobes have the values with respect to the primary lobe of This decreases the first secondary lobe with respect to the primary by 10 decibels at the expense of widening the radiator only 50 per cent to retain the same sharpness of the primary lobe.

Figs. 4 and 5 show two methods of realizing particle velocity distributions of the above and ;able area.

similar types for piezoelectric tive radiating systems, respect 'tric radiator frequently used C1 or an array of substantially salt crystals connected in pa physically to present, substam radiating surface as represen' M, as and it of-Flg. 4;

In one oommon'form the rm all be mounted on a common b, for example, could be placed l crystals of Fig. 4 and have the crystals cemented to it, the crystals forming aradi'ating s An alternate com would be to support all the cry employ radiation from both to or the crystals. The crystals 2 trically inparallel across the 4 later 48.

To reduce the secondary lob suggested above, we can use" arrangements of crystals b1; width of the electrodes, or plat trodes are employed, so that s the crystals it on the ends 1 trodes, or plating areas, when in the center has its sides com the electrodes, and intermedi electrodes of intermediate wid' creasing with proximityto the viding that the plating, or elec same length as the crystals 2 very in width only, the force e: dividual crystal will be propor1 ing or electrode area and the di, portional to the force since a] similar. Hence, if the area of linearly from the two ends of An alternative arrangement, tenuator for each crystal, or ear at a particular distance from array, would be to use crystals trodes but to limit, by interposi suitable amounts, the energy to tals to obtain an approprlatl energy among them.

Fig. 5 shows onerway of obtaii particle velocity distribution l strictlve drive. For this cas diaphragm 50 clamped on the a number of magnetostrictive Since the edges are clamped t and the shape assumed by tl'. vibrating will be nearly that giving the radiation pattern sho The central magnetostrictive course driven most strongly 1 and 56 progressively less strong all energy distribution preferab proportioning the windings of the magnetostrictive members as indicated in Fig. or alternatively by employing attenuators as suggested above for crystal arrays. The magneto-strictive members are connected electricalLv in parallel across the output of an oscillator 58.

In Fig. 6 a sound radiator in the form of a multi-section wave filter having sixteen sections 80, Si, 82, 83, at, 85, 88 and a1 (two sections on opposite sides of the center of the structure be-,- ing assigned the same number) is shown. the left end of the structure a plurality of piezoelectric crystals 9". enclosed in a housing member 89, are employed to energize the structure and at the right end a member 88 of absorbing material is provided to absorb such energy as may reach the right end of the filter.

Each of the sections comprises-a cup-like member of square cross-section, the cup bottoms 82 serving as diaphragms, coupling adiacent cavities. Each section is provided with several holes small portion oi the total energy passing through the filter is radiated. The hole sizes are adjusted so that maximum energy is radiated from the central sections 81 and decreasing amounts of energy from sections, 85, BI, 83, 82, 8i and Bil, respectively, in accordance with their respective distances from the center. Because of attenuation and loss of energy by radiation the sections on the right half of the structure will have somewhat larger holes in order to radiate the same energy as'corresponding sections of the left half of the structure. Again, the distribution of radiated energy may vary from maximum at the central elements to minima at each end in accordance with a straight line, sinusoidal, geometrical progression or other law of variation depending upon the particular performance desired.

The structure of Fig. 6, though of diflerent form and proportions, is of the same general type as that illustrated by Figs. 15, 16 and 1'1 of, and described in, my copending application, Serial No. 381,236, filed March 1, 1941, entitled Pipe antennas and prisms.

Obviously, an array or magnetostrlctive vibratvarying from the central to the end 6 ing members similar to the crystal array 0! m. 4 could be employed without a diaphragm, or, conversely, a plurality of crystals could be employed in place of the magnetostrictive vibrators of Fig. 5 to drive the diaphragm 50, sinusoidally, and numerous other arrangements within the spirit and scope oi the invention can readily be devised by those skilled in the art. No attempt to exhaustively cover such arrangements has here been made. The scope of the invention is defined in the appended claims.

What is claimed is:

1. A piezoelectric radiator comprising a plurality of substantially identical piezoelectric crystals arranged in line, corresponding radiating ends of the crystals lying in a common plane, a pair of electrodes on each crystal. the electrodes extending in every case the full length of the crystals, the width of the electrodes on the end crystals of the line being small with respect to the width of the crystals, the width of eleccrystals being progressively greater as the center of the line is approached, the central crystal or crystals having electrodes of greatest width whereby minor lobe radiation from said array of crystals is substantially reduced.

2. In a directive radiating system a plurality of substantially identical piezoelectric crystals aligned in parallel relation with particular radiating ends of each in a common plane. the electrode plating on each crystal extending the full length of the crystal, the width 0! the plating varying from a small fraction of the width of the crystal for the outermost crystals to substantially the full width or the crystal for the centrally positioned crystal, the variation in plating area following a substantially sinusoidal law of variation. j

3. The radiator of claim 1 the electrode area varying from the central to the end crystals substantially in accordance with a straight line law of variation.

4. The radiator of claim 1 the electrode area crystals substantially in accordance with a power series law of variation.

WARREN P. MASON. 

